Field of the Invention
The present invention relates to an air secondary battery and more specifically to an air secondary battery having a cathode in which a metal oxide is generated in a discharge process.
Description of the Related Art
Air batteries are electric batteries using oxygen as a cathode active material. Air primary batteries using zinc as an anode active material have been widely used, and air secondary batteries, which are rechargeable, have been studied in recent years. In terms of high energy density, using lithium as an anode active material has been attempted in the air secondary batteries. However, as described in Peter G. Bruce, et al., NATURE MATERIALS, vol. 11, no. 1, pp. 19-29 (2012), the conventional air secondary batteries are disadvantageous in that the electric capacitance (or the cyclability) tend to be deteriorated as a result of repeating the charge and discharge cycles and that the overpotential is large in the charge process.
As described in U.S. Pat. No. 8,632,920 and US Patent Application Publication No. 2011/0200891, the above disadvantages are caused because air bubbles stagnate and accumulate on the boundary between the cathode and the electrolyte while the charge and discharge cycles are repeated, whereby the cathode is covered with the air bubbles. To solve this problem, U.S. Pat. No. 8,632,920 proposes that a permeation preventing layer for preventing oxygen permeation is formed on a surface of the cathode that faces the anode.
US Patent Application Publication No. 2011/0200891 proposes a conductive porous body disposed in the cathode. The air bubbles accumulated on the boundary between the cathode and the electrolyte are diffused and removed from the boundary to an oxygen supply port through the conductive porous body.
Furthermore, Japanese Laid-Open Patent Publication No. 2010-257839 discloses an air secondary battery having a cathode wherein the cathode is formed as a stack of first and second layers each having a catalyst, and the pore diameter of the first layer is different from that of the second layer. Therefore, even when the cathode has a large thickness, an oxygen-containing gas can be sufficiently diffused in the cathode.